JP2019205264A - Power unit for welding and output control method - Google Patents

Abstract

To suppress bias magnetism in a transformer resulting from increase and decrease of welding current.SOLUTION: A power unit 50 for welding is provided with: an inverter circuit 52 which is constituted by arranging first to fourth transistors Q1 to Q4 like a bridge to convert DC into AC; a transformer 53 which transforms the AC to be output by the inverter circuit 52; a secondary rectification circuit 54 which rectifies AC to be output by the transformer 53 to output DC; and a control circuit 58 which controls an operation of the inverter circuit 52 so that magnitude of welding current flowing from the secondary rectification circuit to a welding wire approaches a target value, and determines a transistor to be turned on next by the inverter circuit 52 based on a cumulative value of primary side application voltage to be applied from the inverter circuit 52 to a primary side of the transformer 53.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a welding current output control method and a welding power source apparatus.

  As a welding power supply device used in an arc welding apparatus, a direct current input from the primary conversion circuit includes a primary side conversion circuit that rectifies a commercial power supply (for example, a three-phase AC power supply) and converts it into a direct current, and a plurality of switching elements. An inverter circuit that converts high-frequency alternating current into a high-frequency alternating current, a welding transformer (transformer) that converts high-frequency alternating current input from the inverter circuit to a lower pressure, and a low-voltage alternating current input from the welding transformer is rectified and converted to direct current, One having a welding torch and a secondary conversion circuit that outputs to a welding target is known (see Patent Document 1). In Patent Document 1, a full-bridge inverter circuit in which four semiconductor switching elements (transistors or the like) are arranged in a bridge shape is used, and the magnitude of the welding current flowing from the welding torch electrode (welding wire) to the welding object This is adjusted by switching control of the inverter circuit. More specifically, in a full-bridge inverter circuit, two switching elements located diagonally are set as one pair, and a pair to be turned on is alternately switched to convert direct current into alternating current. And the magnitude | size of the alternating current which an inverter circuit outputs is adjusted using the PWM modulation system which adjusts the period (pulse width) which turns on each pair, for example.

JP 2016-144303 A

  In the case of a welding power source device used in an arc welding device, there is no particular problem when the positive and negative are almost balanced in the high-frequency alternating current supplied from the inverter circuit to the transformer. When this occurs, there is a possibility that the magnetism is generated in the transformer. And when a bias magnetism arises in a transformer, there exists a possibility that a switching element may fail in connection with an excessive current flowing into a switching element.

  In particular, in arc welding, control of increasing or decreasing the magnitude of the welding current abruptly according to the state of the droplet formed between the welding wire and the object to be welded (work) in order to suppress the occurrence of spatter and the like. Can be done. When performing such control, the high-frequency alternating current supplied from the inverter circuit to the transformer tends to be biased to the positive side or the negative side.

  Here, in patent document 1, the on-pulse width which turns on each switching element of an inverter circuit is monitored, and the bias of a transformer is suppressed by correcting on-pulse width. However, when performing the above-described control for rapidly increasing or decreasing the magnitude of the welding current, it is difficult to suppress the bias of the transformer.

  An object of this invention is to suppress the magnetic bias in a transformer resulting from the increase / decrease in welding current.

The welding power supply device of the present invention includes a plurality of switching elements constituting a bridge circuit, an inverter circuit that converts direct current into alternating current, a transformer that transforms alternating current output from the inverter circuit, and the transformer A rectifying circuit for rectifying the output alternating current to direct current, control means for controlling the plurality of switching elements in the inverter circuit based on the magnitude of the welding current flowing from the rectifying circuit to the welding wire, and the inverter circuit Determining means for determining a switching element to be turned on next in the inverter circuit based on a cumulative value of the primary side applied voltage applied to the primary side of the transformer.
In such a welding power supply device, the determination means may use an ET product, which is a product of the primary-side applied voltage and the application time of the primary-side applied voltage, as the cumulative value. .
The inverter circuit supplies a positive current to the primary side of the transformer when the first switching element is turned on and the second switching element is turned off, and the first switching element is turned off. In addition, when the second switching element is turned on, a negative current is supplied to the primary side of the transformer, and the determining means is configured to provide the inverter circuit when the accumulated value of the primary side applied voltage is biased to the negative side. The switching element to be turned on next is determined as the first switching element.
Further, the inverter circuit supplies a positive current to the primary side of the transformer when the first switching element is turned on and the second switching element is turned off, and the first switching element is turned off. When the second switching element is turned on, a negative current is supplied to the primary side of the transformer, and the determining means is configured to provide the inverter circuit when the accumulated value of the primary side applied voltage is biased to the positive side. The switching element to be turned on next is determined as the second switching element.
From another point of view, the welding power source device of the present invention includes a first element pair including four switching elements arranged in a bridge shape, and two switching elements located at diagonal positions as a set, and An inverter circuit for converting direct current into alternating current using the second element pair;
Based on the output from the inverter circuit, the transformer that transforms the alternating current output from the inverter circuit, the rectified alternating current output from the transformer, and outputs direct current toward the welding wire For the inverter circuit, the first element pair is turned on and then the second element pair is turned on, the second element pair is turned on and then the first element pair is turned on, or the first element pair is turned on Determining means for deciding whether to turn on the first element pair after turning on, or turn on the second element pair after turning on the second element pair.
Furthermore, from another point of view, the present invention includes a plurality of switching elements constituting a bridge circuit, an inverter circuit that converts direct current into alternating current, a transformer that transforms alternating current output from the inverter circuit, An output control method for a welding power supply apparatus including a rectifier circuit that rectifies alternating current output from the transformer into direct current, the inverter circuit based on a magnitude of a welding current flowing from the rectifier circuit to a welding wire. The plurality of switching elements are controlled, and a switching element to be turned on next in the inverter circuit is determined based on a cumulative value of a primary side applied voltage applied to a primary side of the transformer from the inverter circuit. Yes.
Furthermore, when viewed from another point of view, the present invention provides a first element pair and a second element pair in which four switching elements are arranged in a bridge shape, and two switching elements located diagonally are respectively set. , An inverter circuit that converts direct current into alternating current, a transformer that transforms alternating current output from the inverter circuit, and rectifies the alternating current output from the transformer, and outputs direct current toward the welding wire An output control method for a welding power supply device including a rectifier circuit, wherein an output from the inverter circuit is acquired, and the first element pair is turned on for the inverter circuit based on the output acquired from the inverter circuit. The second element pair is turned on, the second element pair is turned on and then the first element pair is turned on, or the first element pair is turned on and the second element pair is turned on. Or to turn on the element pair, it is characterized by determining, turning on the second element pair after turning on the second element pair.

  According to the present invention, it is possible to suppress the magnetic bias in the transformer due to the increase or decrease of the welding current.

It is a figure showing a schematic structure of a welding system concerning an embodiment of the invention. It is a figure which shows schematic structure of the power supply device for welding in a welding system. It is a figure which shows schematic structure of the control circuit in the power supply device for welding. It is a figure which shows an example of the target value of the output current in short circuit transfer. (A)-(c) is a figure for demonstrating operation | movement of the inverter circuit of this Embodiment. (A)-(c) is a figure for demonstrating the operation | movement (continuation) of the inverter circuit of this Embodiment. (A)-(c) is a figure for demonstrating the operation | movement (continuation) of the inverter circuit of this Embodiment. (A), (b) is a figure for demonstrating ET product. It is a flowchart for demonstrating control of the output current in this Embodiment. It is a figure for demonstrating an example (Example) of a time-dependent change of a total ET product at the time of applying the method of this Embodiment. It is a figure for demonstrating an example (comparative example) of a time-dependent change of a total ET product when not applying the method of this Embodiment.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
[Configuration of welding system]
FIG. 1 is a diagram showing a schematic configuration of a welding system 1 according to an embodiment of the present invention. The welding system 1 performs welding of an object to be welded 200 by a consumable electrode type (melting electrode type) gas shielded arc welding method.

  The welding system 1 includes a welding torch 10 that welds a workpiece 200 using a welding wire 100, and a robot arm 20 that holds the welding torch 10 and sets the position and orientation of the welding torch 10. The welding system 1 also includes a wire feeding device 30 that feeds the welding wire 100 to the welding torch 10 and a shield gas supply device 40 that supplies a shielding gas (for example, carbon dioxide gas) to the welding torch 10. Further, the welding system 1 controls the robot arm 20 and the welding power source device 50 that supplies a direct welding current to the welding wire 100 and the workpiece 200 via the welding torch 10 and controls the welding current. A robot controller 60. Although not described in detail here, the welding power supply device 50 also controls the welding speed, the feeding speed of the welding wire 100, and the like in addition to the welding current.

[Configuration of power supply for welding]
FIG. 2 is a diagram showing a schematic configuration of the welding power supply device 50 in the welding system 1. However, FIG. 2 shows the components related to the supply and control of the welding current extracted from the welding power supply device 50.

  The welding power supply device 50 according to the present embodiment converts the three-phase AC power supplied from the commercial AC power source 5 into DC power by performing various processes, thereby converting the welding torch 10 and the workpiece 200 (see FIG. 1). ). During this time, the welding power supply device 50 adjusts the DC power (DC voltage and DC current) output to the outside by performing various power conversions. In the following description, a welding current output from the welding power supply device 50 to the workpiece 200 (see FIG. 1) via the welding torch 10 and the welding wire 100 is referred to as an output current. is there.

  The welding power supply device 50 of the present embodiment includes a primary rectifier circuit 51, an inverter circuit 52, a transformer 53, a secondary rectifier circuit 54, an output reactor 55, an output current detection circuit 56, and a primary side application. A voltage detection circuit 57 and a control circuit 58 are provided. Hereinafter, each component of the power supply apparatus 50 for welding is demonstrated in order.

(Primary rectifier circuit)
The primary rectifier circuit 51 has an input side connected to the commercial AC power supply 5 and an output side connected to the inverter circuit 52. The primary rectifier circuit 51 converts the three-phase alternating current input from the commercial alternating-current power supply 5 into direct current by rectifying and smoothing. Here, the primary rectifier circuit 51 of the present embodiment is configured by a three-phase full-wave rectifier circuit. More specifically, the primary rectifier circuit 51 of the present embodiment includes a primary rectifier diode group 511 provided on the output side of the commercial AC power supply 5, and an input reactor 512 provided on the output side of the primary rectifier diode group 511. And a smoothing capacitor 513 provided on the output side of the input reactor 512. In this example, the primary rectifier diode group 511 includes six diodes.

(Inverter circuit)
The inverter circuit 52 has an input side connected to the primary rectifier circuit 51 and an output side connected to the transformer 53. The inverter circuit 52 converts the direct current input from the primary rectifier circuit 51 into a single-phase alternating current having a higher frequency than that of the commercial alternating-current power supply 5 by performing a switching process. Here, the inverter circuit 52 of the present embodiment is constituted by a voltage-type full bridge inverter. More specifically, the inverter circuit 52 of the present embodiment includes an input capacitor 521 provided on the output side of the primary rectifier circuit 51 and a switch element group 522 provided on the output side of the input capacitor 521. Yes.

  The switch element group 522 of the present embodiment has a plurality of (here, four) switching elements connected in a bridge shape. More specifically, the switch element group 522 of the present embodiment includes a first transistor Q1, a second transistor Q2, a third transistor Q3, and a fourth transistor Q4, each functioning as a switching element. Here, the first transistor Q1 to the fourth transistor Q4 are not particularly limited, but an IGBT (Insulated Gate Bipolar Transistor) is used in this example. In the present embodiment, the first transistor Q1 and the fourth transistor Q4 function as a first switching element, and the second transistor Q2 and the third transistor Q3 function as a second switching element, respectively.

  In the switch element group 522, the first transistor Q1 and the fourth transistor Q4 are located at one diagonal in the bridge, and the second transistor Q2 and the third transistor Q3 are located at the other diagonal in the bridge. ing. The connection portion between the first transistor Q1 and the third transistor Q3 and the connection portion between the second transistor Q2 and the fourth transistor Q4 are input sides in the switch element group 522. In addition, a connection part between the first transistor Q1 and the second transistor Q2 and a connection part between the third transistor Q3 and the fourth transistor Q4 are output sides in the switch element group 522.

  In addition, the switch element group 522 of the present embodiment includes a first free-wheeling diode D1, a second free-wheeling diode D2, a third free-wheeling diode D3, which are connected in parallel to each of the first transistor Q1 to the fourth transistor Q4. A fourth reflux diode D4 is further included.

(Transformer)
The transformer 53 has an input side connected to the inverter circuit 52 and an output side connected to the secondary rectifier circuit 54. The input side (left side in the figure) is the primary side when viewed from the transformer 53, and the output side (right side in the figure) is the secondary side when viewed from the transformer 53. The transformer 53 converts (transforms) the single-phase alternating current (primary voltage) input from the inverter circuit 52 into a single-phase alternating current (secondary voltage) having a lower voltage value. Here, the transformer 53 of the present embodiment has a magnetic core 530, a primary winding 531, and a secondary winding 532, insulates the primary side from the secondary side, and secondary winding 532. It consists of a single-phase transformer with a center tap on the side.

(Secondary rectifier circuit)
The secondary rectifier circuit 54 as an example of a rectifier circuit has an input side connected to the transformer 53, an output side and a positive side connected to an output reactor 55, and an output side and a negative side connected to an output current detection circuit 56, respectively. Has been. The secondary rectifier circuit 54 converts the single-phase alternating current input from the transformer 53 into direct current by rectifying. Here, the secondary rectifier circuit 54 of the present embodiment is configured by a center tap type single-phase both-wave rectifier circuit that uses the center tap on the secondary side of the transformer 53. More specifically, the secondary rectifier circuit 54 of the present embodiment has a secondary rectifier diode group 541 provided on the output side of the transformer 53. In this example, the secondary rectifier diode group 541 includes two diodes. These two diodes are respectively connected to one end side and the other end side of the secondary winding 532 provided on the output side of the transformer 53, and become the output side and the positive electrode side of the secondary rectifier circuit 54. On the other hand, the middle point of the secondary winding 532 provided on the output side of the transformer 53 is the output side and the negative side of the secondary rectifier circuit 54.

(Output reactor)
The output reactor 55 has an input side connected to the output side and the positive electrode side of the secondary rectifier circuit 54, and an output side connected to the welding wire 100 (see FIG. 1) via the welding torch 10. The output reactor 55 smoothes the waveform of the output current, and the flow of the output current when the welding wire 100 is short-contacted with the workpiece 200 as a base material or when the droplet contacts the molten pool. Is controlled passively. However, the output reactor 55 may be connected to the output side and the negative side of the secondary rectifier circuit 54.

(Output current detection circuit)
The output current detection circuit 56 has an input side connected to the secondary rectifier circuit 54 and an output side connected to the workpiece 200 (see FIG. 1). The output current detection circuit 56 detects a welding current value I that is the magnitude of the output current flowing from the welding torch 10 to the workpiece 200 via the welding wire 100.

(Primary side applied voltage detection circuit)
The primary side applied voltage detection circuit 57 is provided between the output side of the inverter circuit 52 and the input side of the transformer 53, and detects a voltage (inverter output voltage value) output from the inverter circuit 52. Here, in this example, the inverter output voltage value is the same as the primary-side applied voltage value V applied to the primary winding 531 of the transformer 53.

(Control circuit)
The control circuit 58 as an example of the control means and the determination means includes an inverter circuit based on the output current value I detected by the output current detection circuit 56 and the primary side applied voltage value V detected by the primary side applied voltage detection circuit 57. The operation (switching operation) of the first transistor Q1 to the fourth transistor Q4 provided in 52 is controlled.

[Configuration of control circuit]
FIG. 3 is a diagram showing a schematic configuration of the control circuit 58 in the welding power supply device 50. However, FIG. 3 shows an extracted configuration related to the control of the operations of the first transistor Q1 to the fourth transistor Q4 in the control circuit 58. In the following description, among the first transistor Q1 to the fourth transistor Q4 that form a bridge with the switch element group 522 (see FIG. 2), the first and fourth transistors Q1 and Q4 that are located on one diagonal. Is referred to as a first element pair P1, and the second and third transistors Q2 and Q3 located on the other diagonal are referred to as a second element pair P2. In the present embodiment, the first transistor Q1 to the fourth transistor Q4 are turned on / off in units of the first element pair P1 and the second element pair P2. In the present embodiment, the output of the inverter circuit 52 is controlled by a PWM (Pulse Width Modulation) method that modulates the length (pulse width) of the ON period of the first transistor Q1 to the fourth transistor Q4.

  The control circuit 58 according to the present embodiment includes a duty signal creation unit 581, a drive signal creation unit 582, an ET product calculation unit 583, and a total ET product storage unit 584. Hereinafter, each component of the control circuit 58 will be described in order.

(Duty signal generator)
The duty signal creation unit 581 determines the duty ratio in PWM control based on the welding current value I input from the output current detection circuit 56 and the target value of the output current (welding current), and creates a duty signal. . Here, the duty ratio of the present embodiment is determined based on the relationship between the control period and the ON period in the inverter circuit 52, and details thereof will be described later.

(Drive signal generator)
Based on the duty signal input from the duty signal generation unit 581 and the total ET product input from the total ET product storage unit 584, the drive signal generation unit 582 generates the first element pair P1 (first and fourth). A signal for driving the transistors Q1 and Q4 (hereinafter referred to as a first drive signal) and a signal for driving the second element pair P2 (second and third transistors Q2 and Q3) (hereinafter referred to as a second drive signal) (Referred to as drive signal).

(ET product operation part)
The ET product calculation unit 583 applies the primary side application voltage of the transformer 53 based on the duty signal input from the duty signal generation unit 581 and the primary side application voltage value V input from the primary side application voltage detection circuit 57. An ET product determined as a product of the voltage value V and the application time is calculated for each control period. Further, the ET product calculation unit 583 performs an operation of adding (cumulatively) the ET product newly generated in the current control cycle to the total ET product determined as a cumulative value of the past ET product, and updates the total ET product. To do. Details of the ET product will be described later.

(Total ET product storage)
The total ET product storage unit 584 stores the updated total ET product input from the ET product calculation unit 583. Further, the total ET product storage unit 584 outputs the total ET product stored by itself in response to requests from the drive signal creation unit 582 and the ET product calculation unit 583.

[Operation of welding system]
Now, the basic operation of the welding system 1 of the present embodiment will be described.
The primary rectifier circuit 51 converts three-phase alternating current (for example, three-phase 220V, 60 Hz) input from the commercial alternating-current power supply 5 into direct current (for example, about 300V). At this time, in the primary rectifier circuit 51, the primary rectifier diode group 511 performs three-phase full-wave rectification, and the input reactor 512 and the smoothing capacitor 513 perform smoothing after the three-phase full-wave rectification.

  Next, the inverter circuit 52 converts the direct current input from the primary rectifier circuit 51 into a single-phase alternating current (for example, about 10 kHz to 100 kHz) having a higher frequency than the commercial alternating current power supply 5. At this time, in the inverter circuit 52, the input capacitor 521 stabilizes the voltage, and the first element pair P1 and the second element pair P2 (first transistor Q1 to fourth transistor Q4) are on / off controlled. Thus, AC / DC conversion is performed. In addition, the first free-wheeling diode D1 to the fourth free-wheeling diode D4 provided in the inverter circuit 52 serve as escape paths for currents in the opposite directions to the applied voltage in the corresponding first transistor Q1 to fourth transistor Q4. Function.

  Subsequently, the transformer 53 converts the single-phase alternating current input from the inverter circuit 52 into a lower-pressure single-phase alternating current (for example, about several tens of volts).

  Next, the secondary rectifier circuit 54 converts the single-phase alternating current input from the transformer 53 into direct current. At this time, in the secondary rectifier circuit 54, the secondary rectifier diode group 541 performs single-phase both-wave rectification.

  Then, the output reactor 55 smoothes the direct current input from the secondary rectifier circuit 54 and outputs it as an output current. The output current output via the output reactor 55 flows to the workpiece 200 via the welding torch 10 and the welding wire 100. At this time, the tip of the welding wire 100 is melted by an arc to form a droplet, and the grown droplet is detached from the welding wire 100 and transferred to the workpiece 200, and the workpiece 200 is welded. become. As a result, a welded product obtained by welding the workpiece 200 using the welding wire 100 is obtained. During this time, the magnitude of the output current, that is, the welding current value I is increased or decreased according to the control of the inverter circuit 52.

[Target value of output current]
FIG. 4 is a diagram illustrating an example of the target value of the output current in the short circuit transition. In FIG. 4, the horizontal axis represents time t (sec), and the vertical axis represents the target value of the output current, that is, the welding current value I (A). The example shown in FIG. 4 is based on the assumption that the feeding speed is constant.

  In the case of short-circuit transition, the welding wire 100 and the workpiece 200 are short-circuited via a droplet formed at the tip of the welding wire 100, and the droplet is detached from the welding wire 100 and the workpiece 200 is welded. By shifting to the side, an arc state in which an arc is generated between the welding wire 100 and the workpiece 200 is repeated. Here, when the period in which the short-circuit state is maintained is the short-circuit period Tx and the period in which the arc state is maintained is the arc period Ty, the welding cycle Tz is the sum of the short-circuit period Tx and the arc period Ty (Tz = Tx + Ty). Can be expressed as The welding cycle Tz is about 10 (msec) to 30 (msec), and is repeated about 30 to 100 times per second (about 30 Hz to 100 Hz).

  The short circuit period Tx includes a first short circuit period Tx1, a second short circuit period Tx2 following the first short circuit period Tx1, and a third short circuit period Tx3 following the second short circuit period Tx2. Among these, in the first short-circuit period Tx1 where the welding wire 100 and the workpiece 200 start to be short-circuited by the grown droplets, the welding current value I is constant at a low value (however, from the arc second period Ty2 described later). Is set to a large value). Further, the target value is set so that the welding current value I is rapidly increased in the second short-circuit period Tx2 in which the droplet is in the short-circuit state (bridge state) and promotes the formation of the constriction due to the electromagnetic pinch force. Further, in the third short-circuit period Tx3 where the droplet starts to be detached after the constriction is formed, the target value is set so that the welding current value I is rapidly decreased. In the example shown in FIG. 4, the inclination of the target value of the welding current value I is set in two stages in the second short-circuit period Tx2.

  The arc period Ty includes an arc first period Ty1 following the short circuit third period Tx3, and an arc second period Ty2 following the arc first period Ty1 and continuing to the short circuit first period Tx1. Among these, in the arc first period Ty1 in which the current is increased to prevent re-short circuit after the arc re-ignition and the droplet growth is promoted, the target value is set so that the welding current value I is rapidly increased and then gradually decreased. Is set. Further, in the arc second period Ty2 for suppressing spatter scattering at the time of a short circuit, the target value is set so as to be constant while the welding current value I is further reduced.

  The target value of the welding current value I in the present embodiment is always set to be a positive value, and basically, the same waveform is repeatedly output at the welding cycle Tz. However, strictly speaking, the welding cycle Tz cannot be fixed due to the degree of growth of the droplets, etc., and the current peak value and each value are maintained while maintaining the basic shape according to the target value of the average voltage and average current and the short-circuit state. The period width will be adjusted (changed). Here, the target value of the welding current value I depends on the wire diameter of the welding wire 100, but is selected from a range in which the minimum value is several (A) and the maximum value is several hundred (A), for example. In the present embodiment, setting the target value of the output current value I in this way results in the output current value I becoming excessive, for example, when shifting from the short-circuit period Tx to the arc period Ty. Sputtering is suppressed.

[Operation of inverter circuit]
5 to 7 are diagrams for explaining the operation of the inverter circuit 52 according to the present embodiment. Here, FIGS. 5A to 5C, FIGS. 6A to 6C, and FIGS. 7A to 7C show the duty signal Sd output from the duty signal generation unit 581 and the drive, respectively. The first drive signal S1 (for the first element pair P1) and the second drive signal S2 (for the second element pair P2) output from the signal generation unit 582, and the inverter circuit 52 outputs and is input to the transformer 53. The relationship with the primary side applied voltage value V is shown. 5 (a) to 5 (c), 6 (a) to 6 (c), and 7 (a) to 7 (c) respectively show two consecutive cycles of the control cycle Tc of the inverter circuit 52. FIG. ing. Here, the control cycle Tc of the inverter circuit 52 in the present embodiment is a half (half cycle) of the cycle of the single-phase alternating current output from the inverter circuit 52 (0.01 msec to 0.1 msec when the frequency is 10 kHz to 100 kHz). ) Therefore, it can be said that the control cycle Tc of the inverter circuit 52 is sufficiently smaller than the welding cycle Tz (Tc << Tz).

  In general PWM control, a positive output and a negative output are alternately repeated every control cycle Tc. On the other hand, in this embodiment, positive output can be continued or negative output can be continued in addition to alternately performing positive and negative outputs. Here, FIGS. 5A to 5C illustrate a case where a positive output and a negative output are performed in two continuous control cycles Tc. FIGS. 6A to 6C illustrate a case where both positive outputs are performed in two consecutive control cycles Tc. Further, FIGS. 7A to 7C exemplify a case where negative output is performed in two consecutive control cycles Tc.

  In general PWM control, the duty ratio (=) is adjusted by adjusting the on-time Ton for turning on the target element pair (first element pair P1 or second element pair P2) in each control cycle Tc. On time Ton / Control cycle Tc) is set. In PWM control, since the control cycle Tc is constant, the output decreases as the on-time Ton decreases, and the output increases as the on-time Ton increases. Here, FIG. 5A, FIG. 6A, and FIG. 7A exemplify a case where outputs having the same magnitude are performed in two consecutive control periods Tc. FIGS. 5B, 6B, and 7B illustrate a case where the output is decreased in two consecutive control cycles Tc. Furthermore, FIG. 5C, FIG. 6C, and FIG. 7C illustrate a case where the output is increased in two consecutive control periods Tc.

  And in this Embodiment, in control of the inverter circuit 52, it describes in either of these Fig.5 (a)-(c), Fig.6 (a)-(c), Fig.7 (a)-(c). Pattern is used. In the present embodiment, when the first element pair P1 is set on and the second element pair P2 is set off, the direction of the current flowing through the primary winding 531 of the transformer 53 is Define as "positive". Further, in the present embodiment, when the first element pair P1 is set to OFF and the second element pair P2 is set to OFF, the direction of the current flowing through the primary winding 531 of the transformer 53 is It is defined as “negative”.

[ET product]
FIG. 8 is a diagram for explaining the ET product. 8A is a diagram for explaining the ET product when the primary applied voltage value V is positive, and FIG. 8B is a diagram for explaining the ET product when the primary applied voltage value V is negative. It is a figure for doing.

  The ET product is one of the parameters of the transformer 53, and is the product of the voltage (here, the primary applied voltage value V) applied to the transformer 53 and its application time (here, the on time Ton) (in the figure). (Indicated by hatching). The ET product corresponds to the magnetic flux density of the transformer 53 (magnetic core 530). When the primary applied voltage value V is positive (see FIG. 8A), the ET product takes a positive value (+), and when the primary applied voltage value V is negative (see FIG. 8B). In addition, the ET product takes a negative value (−).

[Control of output current]
FIG. 9 is a flowchart for explaining the control of the output current (welding current) of the present embodiment. In the initial state, the value of the total ET product stored in the total ET product storage unit 584 is “0”.

  When welding is started in the welding system 1, the duty signal generation unit 581 acquires the output current value I input from the output current detection circuit 56 (step 10). Next, the duty signal generation unit 581 determines the duty ratio of the current control cycle Tc based on the output current value I acquired in Step 10 and the target value of the output current value I (see FIG. 4) (Step S1). 20). Then, the duty signal creation unit 581 creates a duty signal Sd including the duty ratio of the current control cycle Tc determined in step 20 and outputs the duty signal Sd to the drive signal creation unit 582 and the ET product calculation unit 583.

  Subsequently, the drive signal creation unit 582 reads the total ET product I_ET from the total ET product storage unit 584 (step 30). Then, the drive signal generation unit 582 generates drive signals (first drive signal S1 and second drive signal S2) based on the duty signal Sd input from the duty signal generation unit 581 and the total ET product I_ET read in step 30. ) Is created (step 40). The first drive signal S1 created in step 40 is applied to the first element pair P1 (first and fourth transistors Q1 and Q4), and the second drive signal S2 is applied to the second element pair P2 (second and third elements). The signals are output to the transistors Q2 and Q3), respectively.

Here, the specific contents of step 40 will be described.
In step 40, the drive signal generator 582 first determines whether or not the total ET product I_ET is equal to or less than the negative threshold −th (step 41). When an affirmative determination (Yes) is made in step 41, the drive signal generator 582 sets the output destination of the current control cycle Tc to the first element pair P1 (step 42). On the other hand, if a negative determination (No) is made in step 41, the drive signal creation unit 582 next determines whether or not the absolute value of the total ET product I_ET is equal to or less than the positive threshold value + th ( Step 43).

  When an affirmative determination (Yes) is made in step 43, the drive signal generator 582 determines whether or not the output destination of the previous control cycle Tc was the second element pair P2 (step 44). If an affirmative determination (Yes) is made in step 44, the drive signal generator 582 proceeds to step 42, and sets the output destination of the current control cycle Tc to the first element pair P1. On the other hand, when a negative determination (No) is made in step 43 or step 44, the drive signal creation unit 582 sets the output destination of the current control cycle Tc to the second element pair P2 (step 45).

  Here, when step 42 is selected, the drive signal generation unit 582 sets the first drive signal S1 to ON only for a period corresponding to the duty signal Sd (on period Ton) in the current control cycle Tc. 2 The drive signal S2 is always set to off. On the other hand, when step 45 is selected, the drive signal creation unit 582 sets the first drive signal S1 to be always off in the current control cycle Tc, while the second drive signal S2 is set according to the duty signal Sd. It is set to ON only for the period (ON period Ton). Then, the process proceeds to the next step 50.

  Next, the ET product calculation unit 583 acquires the primary-side applied voltage value V input from the primary-side applied voltage detection circuit 57 (step 50). Next, the ET product calculation unit 583 calculates the ET product et of the current control cycle Tc based on the duty signal Sd input from the duty signal generation unit 581 and the primary side applied voltage value V acquired in step 50. (Step 60). The ET product calculation unit 583 reads the total ET product I_ET from the total ET product storage unit 584 (step 70). Then, the ET product calculation unit 583 adds the ET product et of the current control cycle Tc calculated in step 60 to the total ET product I_ET read in step 70 (I_ET = I_ET + et: step 80). Update the product I_ET. Thereafter, the ET product calculation unit 583 writes the total ET product I_ET updated in step 80 into the total ET product storage unit 584 (step 90), thereby causing the total ET product storage unit 584 to store the total ET product I_ET.

  Then, a determination is made as to whether or not welding has been completed (step 100). If a negative determination (No) is made, the process returns to step 10 to continue the process, and an affirmative determination (Yes) is made. If so, the process ends.

[Concrete example]
FIG. 10 is a diagram for explaining an example (example) of a change with time of the total ET product I_ET when the method of the present embodiment is applied. Here, FIG. 10 shows the relationship among the duty signal Sd, the first drive signal S1, the second drive signal S2, the primary side applied voltage value V, and the total ET product I_ET. In FIG. 10, the horizontal axis indicates the passage of time, and here, 20 continuous control cycles Tc are shown. In FIG. 10, for example, the first control cycle Tc is expressed as [1], and for example, the 20th control cycle Tc is expressed as [20]. These are the same in FIG. 11 described later.

  When the method of the present embodiment is adopted, the output destination, that is, the element to be turned on, is determined by the magnitude relationship between the total ET product I_ET and the thresholds (positive threshold + th, negative threshold−th) for each control cycle Tc. A pair (first element pair P1 or second element pair P2) is determined.

  In the embodiment shown in FIG. 10, basically, the first element pair P1 and the second element pair P2 are alternately selected as output destinations. However, when the total ET product I_ET exceeds the positive threshold + th or the negative threshold −th, depending on the conditions, the first element pair P1 is continuously selected (see [5] to [6]), The second element pair P2 may be continuously selected (see [11] to [13]). Even when the total ET product I_ET exceeds the positive threshold + th or the negative threshold −th, depending on the conditions, the first element pair P1 and the second element pair P2 are alternately selected ([13] to [15 ], [16] to [18]).

  In the embodiment shown in FIG. 10, the total ET product I_ET is temporarily controlled to be close to 0, although it may temporarily exceed the positive threshold + th or the negative threshold -th. That is, control is performed so that the total ET product I_ET falls within the range of the positive threshold + th and the negative threshold + th. Thereby, since the current flowing through the magnetic core 530 of the transformer 53 is less likely to be biased to either positive or negative, the bias magnetism in the transformer 53 is suppressed. In addition, by suppressing the demagnetization in the transformer 53, it is possible to suppress failure of these switching elements due to excessive current flowing through the first transistor Q1 to the fourth transistor Q4 constituting the inverter circuit 52. Become.

[Comparative example]
FIG. 11 is a diagram for explaining an example (comparative example) of a change with time of the total ET product I_ET when the method of the present embodiment is not applied. Here, the waveform of the duty signal Sd shown in FIG. 11 is the same as that shown in FIG.

  When the method of the present embodiment is not adopted, an output destination, that is, an element pair to be turned on (first element pair P1 or second element pair P2) is output for each control cycle Tc regardless of the total ET product I_ET. Determined.

  In the comparative example shown in FIG. 11, the first element pair P1 and the second element pair P2 are always selected alternately as output destinations. Therefore, unlike the embodiment shown in FIG. 10, the first element pair P1 cannot be continuously selected, and the second element pair P2 cannot be continuously selected.

  In the case of the comparative example shown in FIG. 11, the total ET product I_ET is biased toward the negative side as time passes. In this case, since the current flowing through the magnetic core 530 of the transformer 53 is biased negatively, bias magnetism in the transformer 53 is likely to occur. And since it becomes easy to produce the demagnetization in the transformer 53, it becomes impossible to suppress the failure of these switching elements resulting from an excessive current flowing through the first transistor Q1 to the fourth transistor Q4 constituting the inverter circuit 52. .

[Others]
In the present embodiment, the single pulse control that outputs one pulse per control cycle Tc has been described as an example in the PWM control. However, the present invention is not limited to this, for example, two or more per control cycle Tc. Multi-pulse control that outputs pulses may be performed.

  In the present embodiment, the case where the inverter circuit 52 is PWM-controlled has been described as an example, but the present invention is not limited to this. For example, a PPM (Pulse Phase Modulation) method may be adopted.

DESCRIPTION OF SYMBOLS 1 ... Welding system, 10 ... Welding torch, 20 ... Robot arm, 30 ... Wire feeding device, 40 ... Shield gas supply device, 50 ... Power supply device for welding, 51 ... Primary rectifier circuit, 52 ... Inverter circuit, 53 ... Transformer 54 ... secondary rectifier circuit, 55 ... output reactor, 56 ... output current detection circuit, 57 ... primary side applied voltage detection circuit, 58 ... control circuit, 581 ... duty signal creation unit, 582 ... drive signal creation unit, 583 ... ET product calculation unit, 584 ... Total ET product storage unit, Q1 ... first transistor, Q2 ... second transistor, Q3 ... third transistor, Q4 ... fourth transistor, P1 ... first element pair, P2 ... second element versus

Claims (7)

An inverter circuit comprising a plurality of switching elements constituting a bridge circuit and converting direct current to alternating current;
A transformer for transforming alternating current output from the inverter circuit;
A rectifier circuit that rectifies alternating current output from the transformer into direct current;
Control means for controlling the plurality of switching elements in the inverter circuit based on the magnitude of the welding current flowing from the rectifier circuit to the welding wire;
A welding power source apparatus comprising: a determining unit that determines a switching element to be turned on next in the inverter circuit based on a cumulative value of a primary side applied voltage applied to a primary side of the transformer from the inverter circuit.   2. The welding power supply apparatus according to claim 1, wherein the determination unit uses an ET product that is a product of the primary-side applied voltage and an application time of the primary-side applied voltage as the cumulative value. The inverter circuit supplies a positive current to the primary side of the transformer when the first switching element is turned on and the second switching element is turned off, and the first switching element is turned off and the inverter Supplying a negative current to the primary side of the transformer when the second switching element is turned on;
2. The determination unit according to claim 1, wherein when the cumulative value of the primary side applied voltage is biased to the negative side, the switching element to be turned on next in the inverter circuit is determined as the first switching element. 2. The welding power supply device according to 2. The inverter circuit supplies a positive current to the primary side of the transformer when the first switching element is turned on and the second switching element is turned off, and the first switching element is turned off and the inverter Supplying a negative current to the primary side of the transformer when the second switching element is turned on;
2. The determination unit according to claim 1, wherein when the cumulative value of the primary side applied voltage is biased to the positive side, the switching element to be turned on next in the inverter circuit is determined as the second switching element. 4. The welding power supply device according to any one of items 3. An inverter circuit that converts a direct current into an alternating current using a first element pair and a second element pair, each of which includes four switching elements arranged in a bridge shape, and each pair of two switching elements located diagonally;
A transformer for transforming alternating current output from the inverter circuit;
Rectifying the alternating current output from the transformer, and outputting a direct current toward the welding wire; and
Based on the output from the inverter circuit, the first pair of elements is turned on after the first pair of elements is turned on, or the first pair of elements is turned on after the second pair of elements is turned on. Determining means for determining whether to turn on the first element pair after turning on the first element pair, or turning on the second element pair after turning on the second element pair And a power supply for welding. An inverter circuit that includes a plurality of switching elements constituting a bridge circuit, converts direct current into alternating current, a transformer that transforms alternating current output from the inverter circuit, and rectifies alternating current output from the transformer into direct current An output control method for a welding power supply device including a rectifier circuit,
Controlling the plurality of switching elements in the inverter circuit based on the magnitude of the welding current flowing from the rectifier circuit to the welding wire;
An output control method comprising: determining a switching element to be turned on next in the inverter circuit based on a cumulative value of a primary side applied voltage applied from the inverter circuit to a primary side of the transformer. An inverter circuit that converts a direct current into an alternating current using a first element pair and a second element pair, each of which includes four switching elements arranged in a bridge shape, and each pair of two switching elements located diagonally; An output control method of a power supply apparatus for welding, including a transformer that transforms alternating current output from the inverter circuit, and a rectifier circuit that rectifies alternating current output from the transformer and outputs direct current toward a welding wire. There,
Obtaining the output from the inverter circuit;
Based on the output obtained from the inverter circuit, the first element pair is turned on after the first element pair is turned on for the inverter circuit, or the first element is turned on after the second element pair is turned on. Deciding whether to turn on the pair, turn on the first element pair after turning on the first element pair, or turn on the second element pair after turning on the second element pair An output control method characterized by the above.